Abstract
A number of cytokinin analogs containing modifications in the heterocyclic moiety were prepared. These compounds were tested for activity as cytokinins and anticytokinins in the tabacco bioassay and the results were used to determine whether any position(s) of the heterocyclic nucleus of cytokinins may require derivatization as part of an over-all "activation" process. 3-substituted 4-alkylaminopyrazolo [3,4-d]pyrimidines and 4-alkylaminopyrrolo[2,3-d]pyrimidines, for example, have (substituted) carbon rather than nitrogen atoms at positions 3 and 5, respectively (analogous to position 7 in purines) and would be predicted to be metabolically stable at these positions. The finding that these compounds had cytokinin activity suggested that modification at the metabolically stable positions. The finding that these compounds had cytokinin activity suggested that modification at the metabolically stable position, and by extension at position 7 in cytokinin analogues which are purines, is not a prerequisite for the expression of cytokinin activity. Similar consideration of other heterocyclic analogs which have cytokinin activity suggests that the active form of a cytokinin can be the exogenous compound itself. Certain structural analogs of cytokinins were found to inhibit the growth of tobacco callus promoted by 6-(3-methyl-2-butenylamino)purine. These compounds were studied as potential cytokinin antagonists, i.e. having activity analogous to the 7-alkylamino-3-methylpyrazolo[4,3-d]pyrimidines (Hecht, S. M., 2068-2610; Skoog, F., Schmitz, R.Y., Hecht, S.M., and Bock, R. M. (1973) Phytochemistry 12, 25-37). The activity of these compounds is discussed and criteria are proposed to distinguish between those species which are specific anticytokinins and those which otherwise inhibit growth.
Highlights
These compounds were tested for activity as cytokinins and anticytokinins in the tobacco bioassay and the results were used to determine whether any position(s) of the heterocyclic nucleus of cytokinins may require derivatization as part of an over-all “activation” process. 3-Substituted 4
Alkylaminopyrazolo[3,4-dlpyrimidines and 4-alkylaminopyrrolo[2,3-dlpyrimidines, for example, have carbon rather than nitrogen atoms at positions 3 and 5, respectively and would be predicted to be metabolically stable at these positions. The finding that these compounds had cytokinin activity suggested that modification at the metabolically stable position, and by extension at position 7 in cytokinin analogues which are purines, is not a prerequisite for the expression of cytokinin activity
Similar consideration of other heterocyclic analogs which have cytokinin activity suggests that the active form of a cytokinin can be the exogenous compound itself
Summary
These compounds were tested for activity as cytokinins and anticytokinins in the tobacco bioassay and the results were used to determine whether any position(s) of the heterocyclic nucleus of cytokinins may require derivatization as part of an over-all “activation” process. 3-Substituted 4-. The parent member of this series, 4-(3-methyl-2-butenylamino)pyrazolo[3,4-d]pyrimidine [5], which is isomeric with 21, had only about 1% of the growth-promoting activity of the latter, but was an effective cytokinin.
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